leetcode-102 二叉树的层序遍历

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[][]}
 */
var levelOrder = function (root) {
  const result = [];
  if (!root) return result;
  let queue = [root];
  while (queue.length) {
    let newQueue = [];
    const arr = [];
    for (let i = 0; i < queue.length; i++) {
      arr.push(queue[i].val);
      if (queue[i].left) {
        newQueue.push(queue[i].left);
      }
      if (queue[i].right) {
        newQueue.push(queue[i].right);
      }
    }
    result.push(arr);
    queue = newQueue;
  }
  return result;
};